I love singing. I love the fact that there's no external instrument that I have to master, that the voice is within me, the voice is me. And through my voice, I have the opportunity to express whatever I feel. Singing is so inherent to my existence that I can't separate myself from it. I'm always singing; I sing alone, I sing wherever I go. It's almost like a tic - it accompanies me, there's always a tune in my head.

I can't remember a time when I didn't sing. My mother said I used to sing myself to sleep in the cradle, but I never dreamed that my voice would have such a huge significance in my life.

At the age of 17, I was offered a place to study flute at the Royal Academy of Music, which turned out to be both a blessing and a curse. At that point, I hadn't considered using my voice to become a performer. But what I encountered at the Royal Academy left me disillusioned, and led me to subsequently reject training. And that's when I started to explore the notion of singing and songwriting as a complete alternative, inventing my own ideas about it.

Without knowing it, I had picked up the signatures and nuances of hundreds of other voices. As a teenager, I was listening to Motown and the charts, and without realising it, I picked it all up. Being so young, I had no idea how much I was learning. Those songs form the foundation of my musicality, my sound, my nuance. Every song I've ever heard and loved has been indelibly stamped on my heart and brain.

Listening to Joni Mitchell finally made me realise I should become a singer. When I listened to her albums Blue and The Hissing of Summer Lawns, I became fascinated by her poetic lyricism. She managed to describe life and its complexity in visual and psychological terms, and I identified with this; it became a blueprint for me. I was looking for identity. I didn't know who I was, but I knew I didn't want to go back to Scotland and settle for what I'd just run away from. She prompted a revelation; I thought: I could do that, I could sing songs.

When you perform to an audience, no matter how big or small, there's an expectation there. Performing is all about preparation. It's like winding up a film roll or a ribbon before unwinding it. When you step out on stage, you've prepped it up, you're on automatic and it should just unwind naturally. Once you've started, you've got to see it through.

Singing a song is one thing, but expressing a song is another - it's deep. That's why you don't have to be the best singer technically, as long as you can convince people of your emotional authenticity. Performing isn't just about the voice - there's a magic to it, an alchemic quality. All the separate elements add up to something else that's really powerful. It's that something that I'm interested in. A song has the potential to make a person react: to choke up, to want to cry or to want to dance. It's that response that gets me, and everyone can access that.

Once you start a song, you enter a certain zone. You're expressing yourself, and whether you're singing with other people or to other people, it's just so feelgood. When I go to South Africa, I notice that people sing because it's as natural to them as breathing, eating and sleeping. Our culture is so judgmental and repressive that sometimes people lose that.

There is something in singing that is uplifting and freeing of your spirit - there are no rules. Everyone should feel free to sing, like when you're a kid and you skip or do somersaults. You should sing everywhere: when you're in the shower, when you're with your friends. After all, it's completely free.

• Annie Lennox's hits include Walking On Broken Glass and No More I Love You's